Nicotinic acetylcholine receptors (nAChR), which are of a ligand-gated ion channel family, are prevalent in the central nervous system (CNS) and peripheral nervous system (PNS), and are involved in a variety of physiological functions. These receptors serve as important factors in controlling the CNS's physiological functions via controlling the release of a variety of neurotransmitters, such as acetylcholine, norepinephrine, dopamine, serotonin, and gamma-aminobutyric acid (GABA). Therefore, with the control of such neurotransmitters and the cellular signal transfer system, AChR may be used in treating diseases associated with cognitive function, learning and memory, neurodegeneration, pain and inflammation, neuropsychosis and mood disorder, and compulsive and addictive behaviors, controlling and treating inflammation or inflammatory diseases, and in relieving pains.
Diverse nAChR subtypes are present in the CNS and PNS. Typically, nAChR are ionic channels able to selectively transmit diverse cations with five monomers surrounding a central ion conducting pore of the ionic channel. In humans, at least 12 monomers, α2˜α10, and β2˜β4 are expressed, where these monomers form diverse homomeric or heteromeric complexes through combination with each other. Heteromeric α4β2 nAChR with high binding affinity to nicotin and homomeric α7 nAChR with low affinity to nicotin are known to be main expressions in the CNS [Gotti C, Zoli M, Clementi F (2006) Trends in Pharmacol. Sci. 27; 482-491].
Nicotinic α7 receptors, which are expressed in the cerebral cortex and hippocampus that are responsible for brain's cognitive and sensory functions are found both in presynaptic and postsynaptic terminals, and thus, have been suggested as a significant factor in synaptic pass [Burghaus L, Schutz U, Krempel U, de Vos R A I, Jansen Steur E N H, Wevers A, Lindstrom J, Schroder H (2000), Mol. Brain Res. 76; 385-388; Banerjee C, Nyengaard R J, Wevers A, de Vos R A I, Jansen Steur E N H, Lindstrom J, Pilz K, Nowacki S, Bloch W, Schroder H (2000), Neurobiol. Disease, 7; 666-672]. Nicotinic α7 receptors are inherently highly permeable to calcium ions, and thus, have been proposed as a significant factor in diverse calcium-dependent neurotransmission systems [Oshikawa J, Toya Y, Fujita T, Egawa M, Kawabe J, Umemura S, Ishikawa Y (2003) Am. J. Physiol. Cell Physiol. 285; 567-574; Marrero M B, Bencherif M (2009) Brain Res. 1256; 1-7; Ospina J A, Broide R S, Acevedo D, Robertson R T, Leslie F M (1998) J. Neurochem. 70; 1061-1068].
Since nicotinic acetylcholine receptors are involved in the control of various cerebral functions, including cognitive function and attentiveness, substances that are able to directly or indirectly activate such nicotinic acetylcholine receptors are expected to be ultimately beneficial in relieving cognitive impairments, such as Alzheimer type dementia, schizophrenia associated cognitive disorders, and attention deficit such as attention deficit hyperactivity disorder (ADHD) [Levin E D, McClemon F J, Rezvani A H (2006) Psychopharmacology 184; 523-539].